<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        /*
        匹配第一个p标签下的所有span
        */

        p:first-child span{
            font-size: 60px;
            color: red;
        }
    </style>
</head>
<body>
<p><span>aaa</span>bbb</p>
<p>ccc</p>
<p><span>ddd</span>eee</p>
</body>

</html>